1. Field of the Invention
This invention relates to an ejector for use in a refrigeration system in which the efficiency of mixing the primary high velocity fluid or jet and the secondary low velocity fluid is improved by pulsating the primary fluid flow into the diffuser.
2. Description of the Prior Art
The use of ejectors in refrigeration systems has been known for a long time. (See ASHRAE Handbook 1983 Equipment Volume, Chapter 13, "Steam-jet Refrigeration Equipment.") In an ejector, a primary high velocity fluid, such as a steam, gas or vapor jet, is used to entrain and compress, while mixing, a secondary low velocity fluid. This compression process is used in place of mechanical compression to drive a refrigeration system.
Although extremely simple and inexpensive, ejectors are only infrequently used in refrigeration systems due to their low power conversion efficiency. In an ejector, mixing of the primary high velocity fluid jet stream and the secondary fluid stream occurs in the mixing section of the diffuser by shear forces between the two fluid streams. The low power conversion efficiency is due to the dissipation of energy resulting from the friction forces between the primary high velocity fluid stream and the secondary low velocity fluid stream.
To overcome the inherent limitations of the ejector, it is known that the compression process must be an unsteady or intermittent, cyclic process. (See Vermeulen, P.J. et al, "Measurements of Entrainment by Acoustically Pulsed Axisymmetric Air Jets,"Journal of Engineering for Gas Turbines and Power. Vol. 8, July, 1986. Also see Parikh, P.G. et al, "Resonant Entrainment of a Confined Pulsed Jet,"Transactions of the ASME. Vol. 104, December, 1982.)
The use of ejectors in refrigeration systems generally is taught by U.S. Pat. No. 3,427,817. U.S. Pat. No. 2,852,922 teaches an ejector having a primary nozzle through which a primary fluid is introduced into the ejector mixing tube or diffuser and having at least one secondary nozzle. Coolant is introduced through the secondary nozzle into the ejector mixing tube where it mixes with and cools the primary fluid from the primary nozzle. U.S. Pat. No. 3,496,735 teaches an ejector in which the suction pressure for entrainment of the secondary fluid is modulated by a cone shaped control pin axially displaceable in the jet tube portion of the ejector nozzle. U.S. Pat. No. 3,680,327 teaches a steam jet refrigeration apparatus having a compound ejector with a primary jet which accelerates the primary fluid but does little compression and a secondary jet which accomplishes both the mixing of the primary fluid with the secondary fluid and compression of the resulting mixture. U.S. Pat. No. 3,199,310 teaches a thermally powered ejector-type refrigeration system which operates with multiple working fluids of different molecular weights, where the primary fluid or power fluid is of greater molecular weight relative to the secondary fluid or refrigerant fluid. Additional prior art which teaches the use of ejectors in refrigeration systems includes U.S. Pat. No. 3,701,264 which teaches multiple-phase ejectors and controls therefor, U.S. Pat. No. 4,192,148 which teaches a steam-jet apparatus using a one-component refrigerant, and U.S. Pat. No. 4,342,200 which teaches an ejector in an engine cooling system. However, none of the prior art of which I am aware teaches the use of a pulsating ejector for increasing ejector efficiency in a refrigeration system.